What Size Standby Generator Do I Need for a Home?


PowerGeneratorHQ is reader-supported. When you buy through links on our site, we may earn an affiliate commission.

A standby generator is the current ‘must-have’ appliance for many of us, and with good reason. 

It doesn’t matter where you live – an outage can happen at any time. It could be mother nature going wild, or it could be a security breach. 

Regardless, you’ll be affected.

If you find yourself off-grid for just a few minutes, you likely won’t be bothered enough to care. 

But if the outage lasts a few hours or even days, you’ll be more than just a little inconvenienced. 

A standby generator is a great move, but how to get the right one? 

What size standby generator do I need?

What all is it going to power? What fuel source should it run on? Will it be heavily used? 

We cover these issues and more below.

Standby Generator Types You Should Know

Before trying to work out the size, let’s look at the different kinds of generators available on the market.

Gas Standby Generators 

Gas Standby Generators run on either propane or natural gas. Either way, a gas generator is usually connected to a gas line to provide continuous power. 

This is more dependable than having a single fixed-capacity tank of fuel.

At the same time, this makes a gas generator less stable in the event of a natural disaster.

Diesel Standby Generators

Diesel Standby Generators are completely independent of any grid and operate on their own fuel storage. 

The drawback of this is that they’ll require refills more often. Diesel generators are also much louder than gas ones, even when equipped with sound-absorbing enclosures. 

But what makes them a favorite is their sturdiness and longevity. They normally require little maintenance.

Bi-Fuel Standby Generators 

Bi-Fuel Standby Generators aim to use the best of both worlds. A good bi-fuel generator will automatically draw fuel from whichever source is available. 

Some are purpose manufactured as bi-fuel, and others are retrofitted with post-factory adjustments.

How Do They Compare?

Gas Standby Generator Diesel Standby Generator Bi-Fuel Standby Generator
Fuel Propane/ Natural Gas Diesel Propane/ Natural gas/ Diesel
Connection Fix connection to gas line Consume from own fuel storage Draw fuel from whichever source is available
Pros Provide continuous power Completely independent (off grid), less maintenance Flexible
Cons Less stable during natural disaster Need to refill more often, noisy Generally expensive

Consider Your Specific Needs When Choosing A Fuel Type For Your Generator 

generac standby generator

A gas generator is quiet and can also be connected to a stand-alone propane or gas tank.

If your outages are infrequent and don’t last very long, this can be a good solution.

If your area suffers from frequent outages and you expect to use your generator a lot, a diesel-powered one will take more wear and tear.

A standby generator is automatic by its very definition. 

It will turn itself on and off as and when power outages occur, and electricity comes back on, as opposed to portable generators that you need to manually operate.

How Do I Calculate What Size Generator I Need?

There are a few things to consider when deciding on the best size of a standby generator for your home

You need to consider not only what you’ll be using the generator for, but where you live too.

How Big Is Your Home?

The larger the square footage of your home, the more electricity you’ll be using.

In short, the larger the home, the larger the generator required, more so if heating or air conditioning is on your list of requirements.

Where Do You Live?

You may be wondering what this has to do with generator size, but it does matter.

If you live in an area that experiences frequent outages due to bad weather conditions such as rainstorms and hurricanes, you’ll be needing a standby generator with a higher wattage.

A larger sized generator will withstand multiple power surges and outages better and can help prevent further electrical damage caused by stormy weather.

What Do You Need to be Powered?

choose appliances

The rest of your calculation will be based on what exactly you want to be powered up by your standby generator.

Is it the whole house or just a few rooms? Are you opting for essentials only like water supply, or is it to be all appliances?

The smaller the area to be powered, the smaller the generator you will need.

Choosing to power up just your kitchen and bedrooms will require less than powering up the whole house.

If you’re only powering up the lights, fridge, and microwave, you’ll need much less than if you’re backing up the hairdryer, washing machine and oven too. 

So How Many KW Generator Do I Need for My House?

To decide how many kW your generator needs to output, you’ll need to first calculate how much power you need.

Generators are normally rated in watts (W) or kiloWatts (kW), and 1000 watts = 1 kW. 

Choose Your Appliances

A great way to start is by listing your most important circuits. 

Well, pumps, sump pumps, central air, heating, and any medical equipment should top your list. Next in line could be the fridge and freezer.

Once you have your most critical items listed, you can start adding the conveniences you don’t want to live without. 

Adding a few light bulbs won’t add much power usage, nor will a cell phone charger. 

A microwave can cover most of your emergency cooking needs, and radio and TV will keep you posted on alerts and keep you entertained.

It’s Not About Your Appliance’s Physical Size!

It may seem counter-intuitive, but how much power your appliance uses has nothing to do with its physical size. 

A decent fridge may use only 500 watts, while that travel-sized hairdryer may need a hefty 1200 watts.

Write down the power requirements for each item on your list in terms of watts.

There are different ways of stating power consumption, but converting to watts is simple:

  • Watt-hours = watts
  • Kilowatts x 1000 = watts
  • Volts x Amps = watts
  • VA, or volt-amps = watts

So no matter how your appliance states it, converting its power consumption to watts is not rocket science. 

Account for Electrical Motors in Your Appliances

Appliances that use electrical motors will have what is called a starting watt for their motors. 

This is much higher than the normal power usage of the motor and doesn’t last long, but matters when calculating the power output required of a generator.

Check all the items on your list that use an electric motor, and select the one with the highest wattage. 

Multiply its watts by 3, and substitute this result for the original wattage. This will give you the necessary start-up load safety margin.

Calculate Your Power Needs

Total up the watts on the list you just created. Divide your sum total by 1000 to convert to kiloWatts. 

Finally, multiply this by 1.25 to add a safety margin and room for growth. 

So, as an example, if you came up with 17.2 kiloWatts as your required power output, you’ll be looking at an 18-22kW generator to safely and adequately fill your electrical needs during an outage.

Installation Costs for Your Generator

generator installation

Unless you’re a qualified technician with experience, you’re best off hiring a professional company to do the job for you. 

Many reputable companies that sell standby generators also provide consultation services to help you. 

They will help to figure out which type and size of the generator (as well as transfer switch) are best for you and after-sales maintenance too. 

Installing a generator can go anywhere from $500 to $3000. Some experts advise planning for the cost of installation to match the cost of the generator itself. 

A typical home generator installation can set you back $3000-4000, but budget solutions for under $500 are also available. 

What Is the Best Generator for Home Backup?

There are many good generators out there, but after conducting extensive reviews our number one pick is the Generac 70432 Home Standby Generator

Generac 70432 Home Standby Generator Guardian Series 22kW/19.5kW Air Cooled with Wi-Fi and Transfer Switch, Aluminum

Generac has been around a while and has a solid reputation for providing quality generators of all types. 

The Generac 70432 can run on both gas and propane and is the biggest air-cooled standby generator available. 

It also boasts having the lowest cost per kilowatt of any residential generator. For the features it offers, it is also very affordable.

Advantages of Generac 70432 generator:

  • Easy to operate
  • Fuel-efficient
  • Has clean power for sensitive devices (low THD)
  • Has WiFi capabilities
  • Sturdy build, longlasting

The only downside to the Generac 70432 is that it’s on the heavy side, and at 67 dBA at 23 feet, it can be a bit loud. 

It is excellent value for money, however, and can run for longer hours at a time.

It is also big enough to power most homes entirely, letting you use your appliances as normal.

Quick side note: If you don’t need a 22kW generator to power your house, the 10kW standby generator would be sufficient like this one.

Conclusion

Working out what size standby generator you need for your home is not hard, and just takes a small one-time effort on your part. 

Basically, it comes down to listing your critical appliances and calculating their wattage requirements, then adding a bit of a safety and growth margin.

It’s always better to buy a generator above your minimal output requirements. 

You are much more likely to increase your power requirements than the other way round and having a good safety margin never hurts.

If you’re looking for a solid, reliable standby generator that has a good set of features yet is still affordable, we recommend the Generac 70432 Home Standby Generator

Large enough to run most homes entirely, it gives clean, stable power is easy to use, and has a long useful lifespan.